IN a few months, the Four Seasons will launch a Grill Room menu different from the Pool Room’s for the first time in 15 years, says co-owner Julian Niccolini. Meanwhile, new Casa Lever, opening across the street next week, will stake out its territory with a $37, two-course prix-fixe lunch that’s cheaper than most Four Seasons entrees.

Welcome to the Park Avenue power-feeding showdown, Round 2. Of course, everybody denies that either place has anything to prove to the other — “I think all these rivalries are created by the press,” says Niccolini’s partner, Alex von Bidder.

Well, let’s go to town! Because things are simmering at the Seagram Building and Lever House, landmarked office towers whose austere façades give no hint of the culinary cauldrons inside.

In Seagram’s corner is the timeless, Philip Johnson-designed eatery celebrating its 50th year as the capital of rarefied American cuisine for the city’s prime movers. At Lever House across the avenue, enter Casa Lever, an Italian interloper from the owners of beautiful-people-magnet Sant Ambroeus, which has outposts on the Upper East Side, in the Village and in Southampton.

Circumstances and history make it hard not to see it as a return bout between the Seagram and Lever venues. Eater.com co-founder Ben Leventhal said, “It’s always fun to watch the society clubhouses go at each other, but I can’t see this one going to Lever. I think the Casa Lever operators are uniquely qualified to do good business, but the Four Seasons has a 50-year head start on them.”

The first time around, the Four Seasons wrestled the original, modern-American Lever House Restaurant to the asphalt after the latter got off to a blazing start in 2003.

The buzz had Lever picking off the Four Seasons’ customers, especially at lunch when, a New York Magazine story claimed, “The Knives Are Out.” Niccolini clucks of his vanquished challenger: “For the first six months, a lot of our clients went there, and then they came back.”

Lever closed last spring. Its successor opens Monday under new owners and with a new look that mostly banishes the old, argument-starting design I’d praised as a “luxurious submarine” but which Tim Zagat recalls as “like one of those buses that take you out to the plane.”

Casa Lever’s owners say they’ll compete with all the restaurants nearby, including Italian San Pietro and Cellini. But a few months ago, they let it drop which place they had on their minds. Candidates for managers’ jobs were told the Sant Ambroeus team wanted a larger-than-life type to run the front of the house in the style of legendary ringmaster Niccolini himself.

Will Casa Lever siphon off Seasons regulars? “I don’t think anybody defects from the Four Seasons,” said powerful real estate lawyer Jonathan Mechanic, who lunches there. “But it doesn’t mean you go to the same restaurant every day of the week.”

And, he said of Casa Lever, “Aby’s spent time making sure it will be good.” He meant Aby Rosen, the owner of both office towers. He might, if one were to assume a devilish perspective, be inclined to set Lever against Seasons — which opened at Seagram 45 years before he bought it — for sport.

Asked to comment on both places, Rosen first said, “I love Italian food,” and called Casa Lever “the ultimate foodie dream come true.” Prodded, he called Casa Lever “a wonderful complement to the classic Four Seasons, which only gets better and has a marvelous new chef.”

That would be gifted Fabio Trabocchi, the former head chef of Fiamma and the Four Seasons’ first new executive chef in 19 years. He happens to be Italian-born and, adding to the intrigue, was widely reported last spring to be in contention for the Casa Lever job.

Trabocchi denies that, saying Casa Lever owners Gherardo Guarducci and Dimitri Pauli are “two very nice Italian guys” he knew as friends. “We talked, but it was more sharing our thoughts about what to do with their new restaurant” than about his working there. “The rumors were overblown,” he said.

Whether or not Trabocchi’s hiring had anything to do with showing up Lever House, the Four Seasons had needed a new executive chef ever since the death of Christian Albin at age 61 in June.

Not that there’s likely to be any comparison between the two restaurants’ food — Four Seasons classics like bison filet with foie gras and Maryland crab cakes can still thrill, while Sant Ambroeus’s often one-note dishes uptown seem determined not to offend timid palates.

Even so, Albin’s kitchen was lacking the creative edge that once made it a favorite of foodies as well as of movers and shakers. His passing afforded the owners an opportunity to revivify a menu that had become too predictable.

Niccolini seemed to acknowledge that, saying, “We’re looking to make the Four Seasons a much better restaurant than it has been for a while.” Trabocchi isn’t going to Italianize the place, the new chef and both owners say. But Trabocchi notes, “there might be room” for a few more Italian touches “without losing sight that it’s an American restaurant.” His new menu will probably be introduced next month.

Niccolini said of the menus, “We’ll go back to the original way of the Four Seasons. If you eat in the Grill, you won’t be able to get the Pool menu, and vice-versa. They became the same 15 years ago, and we’ll try to go back to the way we were.”

Or, maybe not: Von Bidder said, “The more variety the better — I don’t think we’ve decided on any of this yet.”

Niccolini professes not to think about Casa Lever — “an Italian restaurant, not the old Lever House.”

In fact, Niccolini says, “Our only real concern is the Monkey Bar. It’s competition for us because of all the constant press — not for the food, but for the social scene.”

Casa Lever won’t have a “name” chef, but rather a team of four chefs, three of them from the Milan region. “Chef-driven restaurants are not the Italian approach,” Guarducci said. The menu reads much like those at Sant Ambroeus, but with new crudi and whole-fish categories as well. Prices will be similar, too, with pasta from $18-$26 and entrees from $30-$45.

Casa Lever retains its predecessor’s side booths behind parallelogram-shaped cutouts, but it’s warmer, thanks to new chandeliers and red hues added to the carpet and lounge tabletops. A wall behind the bar that once blocked street views is refreshingly gone. Andy Warhol celebrity portrait prints from Rosen’s collection — a sly parry to the Four Seasons’ art masterpieces — adorn one side of the space.

So, after searching, whom did Casa Lever choose as its front-of-the-house major domo? “Dimitri,” Guarducci declared of his partner.

“I’ll make people start to forget Niccolini,” Pauli laughed.

Both men have a sense of humor about the Four Seasons, but they’re all business about making good on their $3.5 million investment. “We hope their clients will give us a try as an option once in a while,” Guarducci said.

To which Pauli put in with a hearty laugh, “Hopefully five times a week.”